1. Field of the Invention
This invention relates to (I) a drilling fluid containing a new composition of matter resulting from the reaction of (1) substantially water-insoluble polycyclic, polycarboxylic acids obtained as a result of the oxidation of coal with (2) a base and (II) said new composition of matter.
2. Description of the Prior Art
Rotary drilling is a technique that has been commonly used to drill a hole into the earth for the purpose of reaching a gas or oil formation. During this process a drilling fluid is passed downwardly through a rotating drill pipe and through the nozzles of a bit at its lower end, flowed upwardly in the annulus between said drill pipe and the borehole wall and then returned to the surface. The drilling fluid must possess (1) satisfactory viscosity and yield value to rapidly lift drilled formation cuttings to the surface, (2) the ability to plaster effectively the wall of the borehole to minimize drilling fluid leakage into the formation and (3) gel strength sufficient to permit effective suspension of drilled formation cuttings when drilling fluid circulation is interrupted or ceases. Since it is now common to reach formation depths wherein temperatures can be as high as about 150.degree. C., and even higher, it is imperative that drilling fluids be heat stable in order to maintain their desired effectiveness.
A drilling fluid that has been extensively used for a long period of time contains water and a clay, such as bentonite, attapulgite or sepiolite. However, since these drilling fluids are deficient in one or more of the necessary properties enumerated above, it has been the custom to chemically treat such drilling fluids by incorporating therein specific additives to overcome specific deficiencies. Although the treatment of drilling fluids with one or more specific additives can improve some specific properties thereof, such additives can affect other properties of the drilling fluids, requiring the additional incorporation therein of still more additives. Through such development, however, complex mixtures of clay minerals with a large number of interacting chemicals have been produced. Therefore, it has become difficult economically to control the physical and chemical properties of clay-based drilling fluids.
Among the additives that have been suggested for incorporation in aqueous clay-based drilling fluids are the water-soluble alkali metal salts of carboxylated benzene or substituted alkyl benzene, wherein the benzene carries from three to six carboxyl groups, in U.S. Pat. No. 2,545,169 to Salathiel. Crowley et al, in U.S. Pat. No. 2,813,826, subjects a lignitic material to partial oxidation in an aqueous alkaline media, and can incorporate the total product, or the total liquid product, with or without some or all of the water removed therefrom or portions of the liquid product extractable with a strong mineral acid, a low-boiling ether or an alcohol or ketone, in an aqueous clay-based drilling fluid.
Instead of incorporating a large number of additives in an aqueous clay-based drilling fluid, it would be desirable to prepare a simpler drilling fluid containing little or no clay.